1. Technical Field
The present disclosure relates to insulated wires and, in particular, relates to a method of fusing a pair of insulated wires together, and a fused wire made in accordance with such method.
2. Description of the Related Art
Insulated wires are well known for use in many applications, and are formed by coating a metal conductor wire with a coating of insulation material. The metal conductor wire may be an individual wire, or may be a strand made by twisting a plurality of individual metal wires together. Typically, the metal wires are coated by an extrusion process to form a coating or jacket of insulation material around the metal wire.
In some applications, it is desired to manufacture a dual conductor wire in which a pair of insulated metal conductor wires are joined. This dual conductor configuration physically separates, and electrically insulates, the metal conductor wires from one another. Some applications benefit from minimizing the space required to route conducting wires, and a dual conductor wire is generally more compatible with a smaller routing space as compared with two individually routed wires.
Medical applications, such as leads for cardiac rhythm management devices and neurostimulation devices, may require passage of wires through small anatomical channels. Such applications benefit from dual conductor wires, which facilitate passage of the wires through the channels and simplify layout and clamping of the wires before and during a surgical procedure.
One approach to manufacturing insulated dual conductor wires is by co-extruding the insulation material around the pair of conductor wires. However, co-extrusion has certain disadvantages and is not always a desirable method, particularly when forming dual conductor wires that need to be attached along a minimal, or line, contact such that the round cross sectional shapes of the individual insulation coatings of the individual wires is maintained.
In another method, a pair of metal conductor wires are each covered by a coating of insulation by separate extrusion processes. In one version of this method, the coated wires are placed in contact with one another soon after extrusion of the coatings, allowing residual heat from the extruded coatings to fuse the coatings of the wires together. In another version of this method, coated insulated wire pairs are first individually pre-heated, and are then subsequently brought into close contact with one another after heating such that the heated insulation coatings fuse together as the coatings set or cure.
With each of these methods, it is necessary to bring the coated wires as close to one another as possible while the insulation is heated and is not fully cured, and it is very difficult, if not impossible, to avoid deforming the insulation coatings as the wires are pressed together, such that a significant amount of the coating of one wire flows into or around, or blends into, the coating of the other wire, and vice-versa.
These processes tend to produce wires of the type shown in FIG. 1, in which an fused wire 10 made in accordance with the foregoing processes is shown. Fused wire 10 is formed from a pair of separate insulated wires 12a and 12b each including respective conductors 14a and 14b covered by insulation coating 16a and 16b and each having an initial diameter DA, which diameters are shown partially in dashed lines. As may be seen in FIG. 1, when fused wire 10 is formed from a pair of wires 12a and 12b according to one of the above-described processes, significant overlap of the insulation coatings 16a and 16b of the wires 12a and 12b occurs, such that the resulting combined or major diameter DB of the dual fused wire 10 is significantly smaller than the combined initial diameters DA of the individual insulated wires 12a and 12b prior to formation of fused wire 10. In particular, the combined diameter DB of fused wire 10 is often less than 75% of the combined initial diameters DA.
What is needed is a method of fusing a pair of insulated wires to one another, and a wire made in accordance with such method, which is an improvement over the foregoing.